Netherton's syndrome: the importance of eyebrow hair.

Netherton's syndrome (NS) is a rare autosomal recessive disease associated with variable expressions: congenital ichthyosiform erythroderma, ichthyosis linearis circumflexa, specific hair shaft defects (trichorrhexis invaginata) and atopic diathesis. We report the case of 14-year-old non-identical twins whose diagnosis of NS was established on light microscopy of eyebrow hairs. The sisters consulted for a severe episode of atopic dermatitis. Skin examination revealed an ichthyosiform eruption with generalized, polycyclic erythematous plaques with fine double-edged scaling. The flexural creases were lichenified and multiple eczematoid patches were noted. Blood investigation revealed eosinophilia and high IgE level. Microscopy of scalp hair of the twins was repeatedly normal, but the one of the eyebrows revealed typical trichorrhexis invaginata. The presence of trichorrhexis invaginata is necessary to make the diagnosis of NS, but its identification can be difficult because this defect is variable in time and localization. The examination of eyebrow hairs is especially beneficial for patients first seen in late childhood and adults.